JP6230571B2 - Method for producing carbon-silicon composite - Google Patents

Description

  The present invention relates to a method for producing a carbon-silicon composite.

  In order to be used for an IT device and a battery of an automobile, a negative electrode active material of a secondary battery capable of realizing a high capacity and a high output is required. Therefore, silicon attracts attention as a negative electrode active material for high capacity secondary batteries. For example, pure silicon is known to have a high theoretical capacity of 4200 mAh / g.

  However, silicon has not yet been put to practical use because its cycle characteristics are lower than that of carbon-based materials. The reason for this is that, as a negative electrode active material, inorganic particles such as silicon are used as it is for insertion and extraction of lithium. This is because when used as a material, the conductivity between the negative electrode active materials is reduced due to a volume change in the charge / discharge process, or the negative electrode active material is peeled off from the negative electrode current collector. That is, inorganic particles such as silicon contained in the negative electrode active material occlude lithium by charging and expand so that its volume reaches about 300 to 400%. In addition, when lithium is released by discharge, the inorganic particles contract, and when such a charge / discharge cycle is repeated, electrical insulation may occur due to a space generated between the inorganic particles and the negative electrode active material. In addition, since it has a characteristic that the lifetime is rapidly reduced, there is a serious problem in using it for a secondary battery.

  In addition, in terms of initial efficiency, the higher the value obtained by dividing the amount of lithium released when discharging with lithium stored during initial charging, the higher the positive electrode consumed when the initial charge / discharge cycle is performed. Although the amount is small, it is advantageous, but the existing silicon-based negative electrode active material has a problem that the initial efficiency is low.

  Furthermore, in the case of a secondary battery for a vehicle, a high output capable of maintaining the capacity even under severe charge / discharge conditions is required. However, in the case of existing graphite-based and silicon-based negative electrode active materials, a high output is required under severe conditions. In many cases, it cannot be demonstrated.

None

  In order to further improve the initial efficiency, life and output characteristics of the secondary battery, the present invention can disperse the nano-sized Si-block copolymer core-shell carbonized particles well after the primary and secondary carbonization processes. Another object of the present invention is to provide a method for producing a carbon-silicon composite characterized by pulverization.

  However, the technical problem to be solved by the present invention is not limited to the problem mentioned above, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

The present invention includes (a) preparing a slurry solution containing Si-block copolymer core-shell particles, (b) mixing a carbon raw material and the slurry solution to produce a mixed solution, and (c) Crushing the mixed solution after the primary carbonization step to produce a primary carbide; and (d) crushing the primary carbide after the secondary carbonization step. A method for producing a carbon-silicon composite , comprising: producing a secondary carbide , wherein in the step (c), the primary carbonization step is performed at 400 to 600 ° C in the step (d). A secondary carbonization process is performed at 900-1400 degreeC, It is related with the manufacturing method of a carbon-silicon composite_body | complex characterized by the above-mentioned .

  In the step (d), the secondary carbonization process may be performed at a higher temperature than the primary carbonization process.

  In the steps (c) and (d), the pulverization may be performed by a milling method.

  In the step (a), when the 90% cumulative mass particle size distribution diameter of the Si-block copolymer core-shell particles in the slurry solution is D90 and the 50% cumulative mass particle size distribution diameter is D50 1 ≦ D90 / D50 ≦ 1.5, and 2 nm <D50 <160 nm.

  In the step (b), the carbon raw material is at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch, calcined coke, graphene, carbon nanotube, and combinations thereof. One can be included.

  The pitch may have a quinoline insoluble content (QI) of 0 wt% to 20 wt% and a softening point (SP) of 10 ° C. to 120 ° C.

  In step (c), the primary carbonization process may be performed at 400 to 600 ° C. for 1 to 24 hours under 1 to 20 bar.

  In the step (c), when the 90% cumulative mass particle size distribution diameter in the particle distribution of the primary carbide after pulverization is D90 and the 50% cumulative mass particle size distribution diameter is D50, 1 ≦ D90 / D50 ≦ 2.5, and may be 3 μm <D50 <10 μm.

  In the step (d), the secondary carbonization process may be performed at 900 to 1400 ° C. for 0.5 to 24 hours under 0.5 to 20 bar.

  In the step (d), when 90% cumulative mass particle size distribution diameter is D90 and 50% cumulative mass particle size distribution diameter is D50 in the particle distribution of the pulverized secondary carbide, 1 ≦ D90 / D50 ≦ 2 and 3 μm <D50 <10 μm.

  In one embodiment of the present invention, a carbon-silicon composite manufactured by the above method is provided.

  The carbon-silicon composite may have a mass ratio of C to Si of 1:99 to 10:90.

  In another embodiment of the present invention, a negative electrode for a secondary battery comprising a negative electrode current collector coated with a negative electrode slurry containing the carbon-silicon composite, a conductive material, a binder, and a thickener. provide.

  In still another embodiment of the present invention, a secondary battery including the negative electrode for a secondary battery is provided.

  In the present invention, a carbon-silicon composite is manufactured by pulverizing after the primary and secondary carbonization steps, respectively. The manufactured carbon-silicon composite is a nano-sized Si-block copolymer. It is characterized in that the coalesced core-shell carbonized particles are contained in a very uniformly dispersed manner, and when used as a negative electrode active material for a secondary battery, the initial efficiency, life and output characteristics of the secondary battery can be further improved. it can.

2 is a graph showing a distribution of Si-block copolymer core-shell particles measured by a dynamic light scattering method with respect to the slurry solution produced in Example 1. FIG. It is a SEM image with respect to the final carbide | carbonized_material manufactured by the comparative example 3 (FIG. 2 (A)) and Example 1 (FIG. 2 (B)). It is a graph which measures the capacity | capacitance according to discharge rate with respect to the secondary battery manufactured by Examples 1-2 and the comparative example 1, and shows the result of the capacity | capacitance maintenance factor by each discharge rate.

  Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

(Carbon-silicon composite and production method thereof)
The present invention includes (a) preparing a slurry solution containing Si-block copolymer core-shell particles, (b) mixing a carbon raw material and the slurry solution to produce a mixed solution, and (c) Crushing the mixed solution after the primary carbonization step to produce a primary carbide; and (d) crushing the primary carbide after the secondary carbonization step. A method for producing a carbon-silicon composite comprising: producing a secondary carbide.

  The step (a) is a step of preparing a slurry solution including Si-block copolymer core-shell particles.

  The slurry solution includes Si-block copolymer core-shell particles and a dispersion medium, and the Si-block copolymer core-shell particles are centered on the Si core and Si on the surface of the Si core. It has a structure in which a block copolymer shell comprising a block having a high affinity and a block having a low affinity with Si is coated. At this time, the block copolymer shell of the Si-block copolymer core-shell particle is associated with the block having high affinity with Si toward the surface of the Si core due to van der Waals force. , Blocks having low affinity with Si form a spherical micelle structure that associates outward.

  The weight ratio of the Si core to the block copolymer shell is preferably 2: 1 to 1000: 1, and the weight ratio of the Si core to the block copolymer shell is 4: 1 to 20: 1. Although it is more preferable, it is not limited to this. At this time, if the weight ratio of the Si core to the block copolymer shell is less than 2: 1, the content of the Si core that can actually be alloyed with lithium in the negative electrode active material is reduced. There is a problem in that the capacity of the negative electrode active material is lowered and the efficiency of the lithium secondary battery is lowered. On the other hand, when the weight ratio of the Si core to the block copolymer shell exceeds 1000: 1, the content of the block copolymer shell is lowered, and the dispersibility and stability in the slurry solution are lowered. In addition, there is a problem that the block copolymer shell of core-shell carbonized particles cannot sufficiently perform a buffering action in the negative electrode active material.

  The block having a high affinity with Si associates toward the surface of the Si core due to van der Waals force. At this time, the block having a high affinity with Si is polyacrylic. Acid (poly acrylate acid), polyacrylate (poly acrylate), poly methacrylic acid (poly methyl acrylate), polyacrylamide (poly acrylate), carboxy butyl cellulose (Poly vinyl acetate), or polymaleic acid (polymeric acid). Doo is more preferably preferably, polyacrylic acid (poly acrylic acid), but is not limited thereto.

  The block having low affinity with Si associates toward the outside due to van der Waals force or the like, and at this time, the block having low affinity with Si is made of polystyrene (polystyrene). Polyacrylonitrile (polyacrylonitrile), polyphenol (polyphenol), polyethylene glycol (poly ethylene glycol), poly lauryl methacrylate (poly lauryl methacrylate) (poly vinyl difluoride, preferably poly vinyl difluoro) ) Is more preferable, but not limited thereto. At this time, the block having a low affinity with Si is characterized by a higher carbonization yield during carbonization than the block having a high affinity with Si.

  Most preferably, the block copolymer shell is a polyacrylic acid-polystyrene block copolymer shell. At this time, the number average molecular weight (Mn) of the polyacrylic acid is preferably 100 g / mol to 100,000 g / mol, and the number average molecular weight (Mn) of the polystyrene is 100 g / mol to 100,000 g / mol. Although it is preferable that it is mol, it is not limited to this.

  The slurry solution contains silicon particles at a high content, and the Si-block copolymer core-shell particles have a particle distribution within the slurry solution of 90% cumulative mass particle diameter distribution diameter of D90 and 50% cumulative mass particles. When the diameter distribution diameter is D50, 1 ≦ D90 / D50 ≦ 1.5, preferably 2 nm <D50 <160 nm, preferably 1 ≦ D90 / D50 ≦ 1.4, and 2 nm <D50 <120 nm. More preferably, it is not limited to this. The block copolymer shell of the Si-block copolymer core-shell particle forms a spherical micelle structure around the Si core, so that it does not contain another block copolymer. Because of its excellent dispersibility in the slurry solution, the agglomeration phenomenon between the particles is reduced, the D50 in the slurry solution is small, and there is a uniform distribution with a small size deviation between the particles. Copolymer core-shell carbonized particles can be more uniformly and well dispersed within the carbonaceous matrix.

  Various methods for improving dispersion can be used to implement slurry solutions that satisfy the above-described dispersion conditions, about 1 ≦ D90 / D50 ≦ 1.5 and about 2 nm <D50 <160 nm. In particular, various methods may be combined or applied in order to realize a slurry solution satisfying the dispersion condition using silicon powder having a relatively large average particle diameter.

  Explaining exemplarily the method for improving the dispersion, a method for adjusting the type of the dispersion medium, adding an additive for improving the dispersion to the slurry solution, or subjecting the slurry solution to ultrasonic treatment, etc. Can be used. As a method for improving the dispersion, various known methods other than the exemplified methods may be applied, or may be applied in combination.

  The dispersion medium is N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), water, ethanol, methanol, cyclohexanol, cyclohexanone, methyl ethyl ketone, acetone, ethylene glycol, octyne, diethyl carbonate, dimethyl sulfoxide (DMSO) and Any one selected from the group consisting of these combinations can be included.

  Use of the dispersion medium can help the slurry solution to be well dispersed.

  The slurry solution may be subjected to ultrasonic treatment, fine mill treatment, ball mill treatment, three roll mill treatment, stamp mill treatment, in order to realize dispersion characteristics. Various processing methods, such as eddy mill processing, homomixer processing, centrifugal mixer processing, homogenizer processing or vibration shaker processing, etc. Preferably, sonication is more preferable, but not limited thereto.

  Specifically, the ultrasonic treatment may be performed by a method in which the entire slurry solution is simultaneously ultrasonicated by a batch method, or a part of the slurry solution may be circulated continuously. Can be performed in a manner that is continuously sonicated.

  In an apparatus for performing an ultrasonic process, a tip is usually formed, and silicon particles are dispersed using ultrasonic energy emitted from the tip of the chip. Therefore, an area where such ultrasonic energy is transmitted. Has its limits. Therefore, when ultrasonic treatment is performed on a large amount of slurry solution, the slurry solution is continuously circulated so that a part of the slurry solution is continuously ultrasonicated instead of the batch method. The efficiency can be increased by performing ultrasonic treatment in a continuous circulation system. That is, it is possible to process a larger amount of slurry solution by performing ultrasonic treatment in the continuous circulation method for the same power within the same time.

  As an example of specific process conditions, when ultrasonic treatment is performed in a batch system, power of 100 to 500 Watt is supplied to 1000 ml or less of the slurry solution, and can be performed for 30 seconds to 1 hour.

  As another example of specific process conditions, when ultrasonic treatment is performed in a continuous circulation system, a 500 Watt electric power is supplied and ultrasonic treatment is performed for 30 seconds to 1 hour to obtain an amount of about 3600 ml / hr of slurry solution. Can be processed.

  As another example of specific process conditions, ultrasonic treatment may use ultrasonic waves of 10 kHz to 100 kHz, but is not limited thereto.

  The slurry solution produced by simply mixing silicon powder in the dispersion medium aggregates the silicon particles to form a lump, so the average particle size of the silicon particles constituting the slurry solution increases and the silicon particles are uniformly dispersed. It becomes a slurry in an untreated state.

  On the other hand, as described above, the slurry solution can be favorably dispersed by, for example, selecting an appropriate type of dispersion medium or performing an additional process for improving dispersion such as ultrasonic treatment. The distribution characteristics of about 1 ≦ D90 / D50 ≦ 1.5 and about 2 nm <D50 <160 nm can be realized in the slurry solution using silicon particles. That is, even when a powder having an average particle diameter of about 2 nm to about 200 nm, specifically about 60 nm to about 150 nm is used as the silicon powder, a slurry solution in a state of being uniformly dispersed in the dispersion medium is obtained. be able to.

  The step (b) is a step of mixing the carbon raw material and the slurry solution to produce a mixed solution.

  The dispersion medium of the slurry solution can dissolve the carbon raw material. Therefore, the carbon raw material can be dissolved in the slurry solution to prepare a mixed solution.

  Since the carbon raw material is dissolved in the silicon slurry solution, the carbon is subsequently carbonized in a state of capturing the Si-block copolymer core-shell particles in the carbonization step, and is captured and dispersed in the carbonaceous matrix. -A carbon-silicon composite containing block copolymer core-shell carbonized particles can be formed.

  The carbon raw material is a starting material for forming a carbonaceous matrix, and can be used without distinguishing between conductive and non-conductive cases, natural graphite, artificial graphite, soft carbon, At least one selected from the group consisting of hard carbon, pitch, coke, graphene, carbon nanotube, and combinations thereof may be included. Specifically, as the carbon raw material, generally, coal-based coal tar pitch or petroleum-based pitch can be obtained and used. At this time, it is preferable to use a pitch having a quinoline insoluble content (QI) of 0 wt% to 20 wt% and a softening point (SP) of 10 ° C. to 120 ° C. as the carbon raw material. Not.

  The carbon raw material is carbonized by a subsequent carbonization process to form a carbonaceous matrix including crystalline carbon, amorphous carbon, or all of them.

  The step (c) is a step of producing a primary carbide by pulverizing the mixed solution after the primary carbonization step.

  In the present invention, the “carbonization process” means a process in which a carbon raw material is baked at a high temperature to remove inorganic substances and leave carbon.

  The primary carbonization step is preferably performed at a temperature lower than that of the secondary carbonization step, and more preferably performed at 400 to 600 ° C. for 1 to 24 hours under 1 to 20 bar, but is not limited thereto. When the primary carbonization step is performed at a temperature lower than 400 ° C., there is a problem that impurities other than carbon in the carbon raw material are not removed. When the temperature is higher than 600 ° C., a large amount of impurities are scattered at a time. There are difficulties in the processing process.

  At this time, the carbonization yield in the primary carbonization step may be 40 to 80% by weight. By increasing the carbonization yield in the primary carbonization step, the generation of volatile matter can be reduced, the treatment can be facilitated, and the process can be friendly to the environment.

  After the primary carbonization step, the pulverization may be performed by a known method, and is preferably performed by any one method selected from the group consisting of grinding, mixing, and milling. More preferably, the method is not limited to this. Specific milling methods include a fine mill, a ball mill, a three roll mill, a stamp mill, an eddy mill or a jet mill. It is preferable to use any one method selected from the group consisting of, and more preferably, but not limited to, the use of a zet mill method.

  As can be confirmed in Comparative Examples 2 and 3 of the present invention, the initial efficiency of the secondary battery is better as a result of pulverization by the zet mill method than in the result of pulverization by the ball mill method.

  At this time, when the 90% cumulative mass particle diameter distribution diameter of the primary carbide after pulverization is D90 and the 50% cumulative mass particle diameter distribution diameter is D50, 1 ≦ D90 / D50 ≦ 2.5 Yes, it may be 3 μm <D50 <10 μm.

  By pulverization after the primary carbonization step, the pulverization efficiency can be increased by performing pulverization when the state of the carbide is somewhat flexible. By forming uniform particles, the initial efficiency of the secondary battery and The output characteristics can be further improved.

  The step (d) is a step of manufacturing the secondary carbide by pulverizing the primary carbide after the secondary carbonization step.

  The secondary carbonization step is preferably performed at a higher temperature than the primary carbonization step, and more preferably performed at 900 to 1400 ° C. for 1 to 24 hours under 1 to 20 bar, but is not limited thereto. When the secondary carbonization step is performed at a temperature lower than 900 ° C., there is a problem that impurities or functional groups other than carbon in the carbon raw material are not completely removed. When the secondary carbonization step is performed at a temperature higher than 1400 ° C., silicon-carbon particles Generation of silicon and melting of silicon occur.

  At this time, the carbonization yield in the secondary carbonization step is preferably 80% by weight or more, and more preferably 90% or more, but is not limited thereto. That is, the carbonization yield in the secondary carbonization process is higher than the carbonization yield in the primary carbonization process.

  The pulverization method after the secondary carbonization step is as described above for the pulverization method after the primary carbonization step.

  That is, as can be confirmed in Comparative Examples 2 and 3 of the present invention, the initial efficiency of the secondary battery is better as a result of pulverization by the zet mill method than by pulverization by the ball mill method.

  At this time, when the 90% cumulative mass particle size distribution diameter in the particle distribution of the secondary carbide after pulverization is D90 and the 50% cumulative mass particle size distribution diameter is D50, 1 ≦ D90 / D50 ≦ 2. It may be 3 μm <D50 <10 μm.

  By forming uniform particles by pulverization after the primary carbonization step, the initial efficiency and output characteristics of the secondary battery can be further improved.

  That is, as in the method for producing a carbon-silicon composite according to the present invention, when pulverization is performed after the primary and secondary carbonization steps, unpulverized material is removed, the particle diameter is uniform, and the surface is Round particles can be obtained. As a result, the generation of particles having a rough surface during the initial charge / discharge and the side reaction caused by the unpulverized product can be reduced, and the initial efficiency can be increased. Note that when the particles are close to a sphere and the surface bending is reduced, the insertion / release of lithium is performed rapidly, so that the output characteristics can be further improved.

  The present invention also provides a carbon-silicon composite produced by the above method.

  The carbon-silicon composite manufactured by the method for manufacturing the carbon-silicon composite is formed by the Si-block copolymer during the manufacturing process in which the Si-block copolymer core-shell carbonized particles form a composite with the carbonaceous matrix. The core-shell carbonized particles are not agglomerated so that the Si-block copolymer core-shell carbonized particles are not largely agglomerated and formed so as to be uniformly and well dispersed in the carbonaceous matrix. In this way, the Si-block copolymer core-shell carbonized particles may be uniformly dispersed throughout the carbonaceous matrix of the carbon-silicon composite. Such a carbon-silicon composite, when applied to a negative electrode active material for a lithium secondary battery, effectively exhibits high-capacity silicon characteristics, enhances initial efficiency, and expands during charge and discharge. By alleviating this problem, the life characteristics of the lithium secondary battery can be improved. Further, it is possible to improve output characteristics capable of expressing a high capacity even under severe discharge conditions, that is, when the discharge rate is high.

  Even if the carbon-silicon composite in which the Si-block copolymer core-shell carbonized particles are more uniformly and well dispersed contains the same content of silicon, a more excellent capacity can be realized. For example, it can be implemented to about 80% or more of the theoretical silicon capacity.

  Specifically, the carbon-silicon composite may be formed into a spherical or nearly spherical particle, and the carbon-silicon composite may have a particle diameter of 0.5 μm to 50 μm. The carbon-silicon composite having a particle size in the above range effectively exhibits the charge capacity due to the high-capacity silicon characteristics when applied as a negative electrode active material of a lithium secondary battery, and enhances the initial efficiency and charge / discharge. In this case, the life and output characteristics of the lithium secondary battery can be improved by alleviating the problem of volume expansion.

  The carbon-silicon composite preferably has a mass ratio of C to Si of 1:99 to 10:90, but is not limited thereto. The carbon-silicon composite has the advantage that it can contain silicon at a high content even within the above numerical range, because it contains a high content of silicon and the silicon particles are well dispersed. In addition, the problem of volume expansion during charge / discharge, which is a problem when silicon is used as the negative electrode active material, can be improved.

  At this time, since the carbon-silicon composite contains almost no oxide that can deteriorate the performance of the secondary battery, the content of oxygen (O) is very low. Specifically, the core layer may have an oxygen (O) content of 0 wt% to 1 wt%. The carbonaceous matrix contains almost no other impurities and by-product compounds and is substantially composed of carbon. Specifically, the carbonaceous matrix has a C content of 70 wt% to 100 wt%. %.

(Anode for secondary battery)
The present invention provides a negative electrode for a secondary battery formed by coating a negative electrode current collector with a negative electrode slurry containing the carbon-silicon composite, a conductive material, a binder, and a thickener.

  The negative electrode for a secondary battery is formed by coating a negative electrode slurry containing the carbon-silicon composite, a conductive material, a binder, and a thickener on a negative electrode current collector, followed by drying and rolling. .

  As the conductive material, any one or more selected from the group consisting of a carbon-based material, a metal material, a metal oxide, and an electrically conductive polymer can be used. Specifically, carbon black, acetylene Black, ketjen black, furnace black, carbon fiber, fullerene, copper, nickel, aluminum, silver, cobalt oxide, titanium oxide, polyphenylene derivatives, polythiophene, polyacene, polyacetylene, polypyrrole, polyaniline, and the like can be used.

  Examples of the binder include styrene-butadiene rubber (SBR, Styrene-Butadiene Rubber), carboxymethyl cellulose (CMC), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (polyvinyl). ), Polyacrylonitrile, polymethylmethacrylate, and the like, and the thickener is used for viscosity adjustment, and includes carboxymethylcellulose and hydroxymethylcellulose. Hydroxyethyl cellulose and Hydroxypropyl cellulose and the like can be used.

  As the negative electrode current collector, stainless steel, nickel, copper, titanium, or an alloy thereof can be used, and among these, copper or a copper alloy is most preferable.

  The weight ratio of the carbon-silicon composite: conductive material: binding material: thickener may be 70 to 91: 5 to 10: 2 to 10: 2 to 10.

(Secondary battery)
The present invention provides a secondary battery including the negative electrode for a secondary battery.

  The secondary battery uses a carbon-silicon composite containing nano-sized Si-block copolymer core-shell carbonized particles dispersed very uniformly as a negative electrode active material for a secondary battery. It is characterized by improved life characteristics.

  The secondary battery is formed to include the secondary battery negative electrode, a positive electrode including a positive electrode active material, a separation membrane, and an electrolytic solution.

Examples of the material used as the positive electrode active material may be LiMn ₂ O _4, LiCoO _2, such as LiNiO _2, LiFeO _2, it absorbs lithium, and compounds capable of releasing is used.

  As a separation membrane that insulates the electrode between the negative electrode and the positive electrode, an olefin-based porous film such as polyethylene or polypropylene can be used.

Examples of the electrolyte include propylene carbonate, ethylene carbonate, butylene carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolane, 4-methyldioxolane, N, N-dimethylformamide, dimethylacetamide, Dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl Carbonate, diethylene glycol, or di One or more aprotic solvents such as _{Chirueteru, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiClO 4, LiCF 3 SO 3, Li (CF 3 SO 2) 2 N, LiC 4 F 9 SO 3, _{LiSbF 6, LiAlO 4, LiAlCl 4} , LiN (C x F 2x + 1SO 2) (C y F 2y + 1SO 2) ( however, x, y are natural numbers), LiCl, one or more of lithium salts, such as LiI A solution in which an electrolyte is mixed and dissolved can be used.

  A medium- and large-sized battery module or a battery pack including a large number of the secondary batteries that are electrically connected to each other can be provided. The medium- or large-sized battery module or the battery pack includes a power tool; an electric vehicle. Electric vehicle including: Vehicle, EV), Hybrid Electric Vehicle (HEV), Plug-in Hybrid Electric Vehicle (PHEV); Electric Truck; Electric Commercial Vehicle; or Power Storage It can be used as a medium power device for any one or more of the system.

  Hereinafter, in order to easily understand the present invention, preferred examples are presented. However, the following examples are provided for easier understanding of the present invention, and the contents of the present invention are not limited by the following examples.

[Example]
Example 1
(Manufacture of negative electrode active materials for secondary batteries)
A polyacrylic acid-polyacrylonitrile block copolymer was synthesized by the reversible addition-fragmentation chain transfer method of polyacrylic acid and polyacrylonitrile. At this time, the number average molecular weight (M _n ) of polyacrylic acid is 4090 g / mol, and the number average molecular weight (M _n ) of polyacrylonitrile is 29370 g / mol. 0.25 g of polyacrylic acid-polyacrylonitrile block copolymer was mixed with 44.75 g of N-methyl-2-pyrrolidone (NMP) dispersion medium. To 45 g of the mixed solution, 5 g of Si particles having an average particle diameter of 50 nm was added. A slurry solution was prepared by treating the solution to which the Si particles were added with an ultrasonic horn for 20 minutes with an ultrasonic wave of 20 kHz. At this time, as a result of measuring the distribution characteristics of the Si-block copolymer core-shell particles with respect to the slurry solution by a dynamic light scattering method (measuring instrument: ELS-Z2, manufactured by Otsuka Electronics), D90 / D50 was 1.37 and D50 was 92.8 nm.

  As a carbon raw material, 120 g of pitch (QI: 4 wt%, SP: 30 ° C.) and 34 g of the slurry solution were mixed and dispersed, and then distilled to remove NMP. Next, after primary carbonization at 500 ° C. under 7 bar for 6 hours, primary grinding by a jet-mill method, particles having D90 / D50 of 2.15 and D50 of 7.7 μm A primary carbide having a distribution was produced. Next, secondary carbonization was performed at 1000 ° C. for 1 hour under 1 bar, and then secondary pulverization was performed by a jet-mill method. The pulverization yield was 90% or more, and D90 / D50 was 1.76. A carbon-silicon composite was manufactured by manufacturing a secondary carbide having a particle distribution with a D50 of 7 μm. At this time, the carbon-silicon composite has a mass ratio of C to Si of 4:96.

(Manufacture of negative electrode for secondary battery)
The carbon-silicon composite: carbon black (CB): carboxymethyl cellulose (CMC): styrene butadiene (SBR) was mixed with water at a weight ratio of 91: 5: 2: 2 to prepare a negative electrode slurry composition. . This was coated on a copper current collector and dried and rolled in an oven at 110 ° C. for about 1 hour to produce a negative electrode for a secondary battery.

(Manufacture of secondary batteries)
The negative electrode for a secondary battery, a separation membrane, an electrolyte solution (1.0M LiPF ₆ added as a mixed solvent of ethylene carbonate: dimethyl carbonate (1: 1 weight ratio)), a lithium electrode, and a coin cell are sequentially stacked. cell) type secondary battery was manufactured.

(Example 2)
Although it carried out on the same conditions as Example 1, it carbonized for 1 hour at 1100 degreeC, and the carbon-silicon composite_body | complex, the negative electrode for secondary batteries and the secondary battery which applied this were manufactured.

(Example 3)
The same conditions as in Example 1 were used except that a carbon-silicon composite and a negative electrode for a secondary battery and a secondary battery to which the carbon-silicon composite was applied using pitch (QI: 0 wt%, SP: 110 ° C.) as a carbon raw material Manufactured.

(Comparative Example 1)
Although it carried out on the same conditions as Example 1, it carbonized for 1 hour at 850 degreeC, and the carbon-silicon composite_body | complex, the negative electrode for secondary batteries and the secondary battery which applied this were manufactured.

(Comparative Example 2)
Although the same conditions as in Comparative Example 1 are used, the primary pulverization after the primary carbonization step is omitted, and after the secondary carbonization step, pulverization is performed by a ball-milling method. The applied secondary battery negative electrode and secondary battery were manufactured. At this time, the particle distribution of the secondary carbide is 50 μm or less, and the pulverization yield is 60% or less.

(Comparative Example 3)
Although the same conditions as in Comparative Example 1 are used, the primary pulverization after the primary carbonization step is omitted, and after the secondary carbonization step, pulverization is performed by a jet-milling method. The applied secondary battery negative electrode and secondary battery were manufactured. At this time, the particle distribution of the secondary carbide is D50 = 7.9 μm, and the pulverization yield is 30% or less.

(Comparative Example 4)
Although it carried out on the same conditions as the comparative example 1, the primary carbonization process was abbreviate | omitted and the negative electrode for secondary batteries and secondary battery which applied this, and the carbon-silicon composite_body | complex were manufactured.

(Experimental example 1)
The secondary battery manufactured in Examples 1 to 3 and Comparative Examples 1 to 4 was subjected to charge / discharge experiments under the following conditions.

  Assuming that 300 mA per 1 g weight is 1 C, the charging condition is controlled at a constant current of 0.2 V to 0.01 V, the constant voltage from 0.01 V to 0.01 C, and the discharging condition is up to 1.5 V at 0.2 C. Measured at a constant current.

  Table 1 shows the results of the discharge capacity retention rate (%) after 25 cycles in which the discharge capacity retention rate after 25 cycles is converted to% with respect to the initial efficiency and initial discharge capacity obtained by dividing the initial discharge capacity by the initial charge capacity. It was described in.

  Referring to Table 1, the secondary batteries manufactured in Examples 1 to 3 were subjected to primary pulverization by a jet-mill method after the primary carbonization step, and the secondary carbonization step was performed at 1000 ° C. or higher. As a result of using the carbon-silicon composite produced and used as the negative electrode active material, it can be confirmed that the initial efficiency has been greatly improved. On the other hand, the secondary carbonization step is performed at less than 1000 ° C. as in Comparative Example 1. When performed, the carbon crystallinity is low, the instability is increased, and the initial efficiency is decreased.

  In the secondary batteries manufactured in Comparative Examples 2 to 3, when the primary pulverization was omitted along with the influence of temperature in the secondary carbonization step, the final carbide particle distribution was not uniform, and a large amount of unpulverized particles existed. Therefore, the initial efficiency was significantly lower than that of Comparative Example 1.

  FIG. 2 is an SEM image of the final carbide produced in Comparative Example 3 (FIG. 2A) and Example 1 (FIG. 2B). Referring to FIG. 2, the final carbide produced in Comparative Example 3 (FIG. 2A) has a more uniform particle distribution than the final carbide produced in Example 1 (FIG. 2B). In addition, it can be confirmed that a large amount of unpulverized particles are present.

  The secondary batteries manufactured in Comparative Examples 1 to 3 can be confirmed to have significantly improved the problem of reduction in discharge capacity even after 25 cycles as a result of performing all the primary and secondary carbonization steps. In Comparative Example 4 manufactured by omitting the primary carbonization step and performing only the secondary carbonization step, the discharge capacity is greatly reduced after 25 cycles, and the capacity reduction typically generated when using silicon is reduced. A problem appeared.

  On the other hand, in the case of pitch as a carbon raw material, the results of charging and discharging differ depending on the content of quinoline insoluble matter (QI) and the softening point (SP), but the quinoline insoluble content (QI) is 0 to 4% by weight. When the softening point (SP) is 30 to 110 ° C., the results show that the initial efficiency and life characteristics of the secondary battery are improved.

In particular, the secondary battery manufactured in Example 1 has a quinoline insoluble content (QI) of 4 wt% and a pitch having a softening point (SP) of 20 ° C., after the primary carbonization step, When the carbon-silicon composite produced by performing primary pulverization, secondary carbonization process at 1000 ° C. and then secondary pulverization is used as the negative electrode active material, the initial efficiency and life characteristics of the secondary battery are further improved. It was confirmed that it could be improved.

(Experimental example 2)
With respect to the secondary batteries manufactured in Examples 1 and 2 and Comparative Example 1, the characteristics by discharge rate were evaluated under the following conditions. Assuming that 300 mA per 1 g weight is 1 C, the charging conditions are controlled at 0.2 C to a constant current of 0.01 V, 0.01 V to a constant voltage of 0.01 C, and the discharging conditions are 0.2 C, 0.5 C, Measurement was performed at a constant current up to 1.5 V for 5 cycles each at 1C and 2C.

  FIG. 3 is a graph showing the results of capacity retention ratios for the secondary batteries manufactured in Examples 1 and 2 and Comparative Example 1 by measuring the capacity for each discharge rate.

  Referring to FIG. 3, the secondary batteries manufactured in Examples 1 and 2 have a high capacity retention rate even when the discharge rate is gradually discharged from 0.2 C to 2 C under severe conditions. As for the secondary battery manufactured by (2), the capacity maintenance rate decreased from 0.2C, and the capacity maintenance rate suddenly decreased at 2C.

  That is, when performing a secondary carbonization process at high temperature of 1000 degreeC or more, it has confirmed that the output characteristic of a secondary battery could be improved more.

  The above description of the present invention is for illustrative purposes, and any person having ordinary knowledge in the technical field to which the present invention belongs can be used without changing the technical idea and essential features of the present invention. It can be understood that it can be easily transformed into other specific forms. Accordingly, it should be understood that the embodiments described above are illustrative in all aspects and not limiting.

Claims (9)

(A) providing a slurry solution comprising Si-block copolymer core-shell particles;
(B) mixing the carbon raw material and the slurry solution to produce a mixed solution;
(C) performing a pulverization after the primary carbonization step on the mixed solution to produce a primary carbide;
(D) a method of producing a carbon-silicon composite, comprising the step of grinding the primary carbide after the secondary carbonization step to produce the secondary carbide,
In step (c), the primary carbonization step, 4 00-600 ° C., in step (d), second carbonization step is characterized by dividing the line at 9 00 to 1400 ° C., carbon - silicon A method for producing a composite. The method according to claim 1, wherein in the steps (c) and (d), the pulverization is performed by a milling method. In the step (a), when the 90% cumulative mass particle size distribution diameter of the Si-block copolymer core-shell particles in the slurry solution is D90 and the 50% cumulative mass particle size distribution diameter is D50 2. The method for producing a carbon-silicon composite according to claim 1, wherein 1 ≦ D90 / D50 ≦ 1.5 and 2 nm <D50 <160 nm. In the step (b), the carbon raw material is at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, hard carbon, pitch, calcined coke, graphene, carbon nanotube, and combinations thereof. The method for producing a carbon-silicon composite according to claim 1, comprising: The method for producing a carbon-silicon composite according to claim 4, wherein the pitch has a quinoline insoluble content (QI) of 0 wt% to 20 wt% and a softening point (SP) of 10 ° C to 120 ° C. In the step (c), when the 90% cumulative mass particle size distribution diameter in the particle distribution of the primary carbide after pulverization is D90 and the 50% cumulative mass particle size distribution diameter is D50, 1 ≦ D90 / D50 ≦ The method for producing a carbon-silicon composite according to claim 1, wherein 2.5 and 3 μm <D50 <10 μm. In the step (d), when 90% cumulative mass particle size distribution diameter is D90 and 50% cumulative mass particle size distribution diameter is D50 in the particle distribution of the pulverized secondary carbide, 1 ≦ D90 / D50 ≦ The method for producing a carbon-silicon composite according to claim 1, wherein 2 and 3 μm <D50 <10 μm. 2. The method for producing a carbon-silicon composite according to claim 1, wherein in the step (c), the primary carbonization step is performed at 1 to 20 bar for 1 to 24 hours. 9. The method for producing a carbon-silicon composite according to claim 1, wherein in the step (d), the secondary carbonization step is performed at 1 to 20 bar for 1 to 24 hours.